Characteristics and properties of metal aluminum thin films prepared by electron cyclotron resonance plasma-assisted atomic layer deposition technology

Metal aluminum （A1） thin films are prepared by 2450 MHz electron cyclotron resonance plasma-assisted atomic layer deposition on glass and p-Si substrates using trimethylaluminum as the precursor and hydrogen as the reductive gas. We focus our attention on the plasma source for the thin-film preparation and annealing of the as-deposited films relative to the surface square resistivity. The square resistivity of as-deposited A1 films is greatly reduced after annealing and almost reaches the value of bulk metal. Through chemical and structural analysis, we conclude that the square resistivity is determined by neither the contaminant concentration nor the surface morphology, but by both the crystallinity and crystal size in this process.

Effect of source temperature on phase and metal–insulator transition temperature of vanadium oxide films grown by atomic layer deposition

Vanadium oxide films were grown by atomic layer deposition using the tetrakis[ethylmethylamino] vanadium as the vanadium precursor and H2O as the oxide source. The effect of the source temperature on the quality of vanadium oxide films and valence state was investigated. The crystallinity, surface morphology, film thickness, and photoelectric properties of the films were characterized by x-ray diffraction, atomic force microscope, scanning electron microscope, I–V characteristics curves, and UV–visible spectrophotometer. By varying the source temperature, the content of V6O11, VO2, and V6O13 in the vanadium oxide film increased, that is, as the temperature increased, the average oxidation state generally decreased to a lower value, which is attributed to the rising of the vapor pressure and the change of the ionization degree for organometallics. Meanwhile, the root-mean-square roughness decreased and the metal–insulator transition temperature reduced. Our study is great significance for the fabrication of vanadium oxide films by atomic layer deposition.

Atomic layer deposition for nanoscale oxide semiconductor thin film transistors:review and outlook

Since the first report of amorphous In–Ga–Zn–O based thin film transistors,interest in oxide semiconductors has grown.They offer high mobility,low off-current,low process temperature,and wide flexibility for compositions and processes.Unfortunately,depositing oxide semiconductors using conventional processes like physical vapor deposition leads to problematic issues,especially for high-resolution displays and highly integrated memory devices.Conventional approaches have limited process flexibility and poor conformality on structured surfaces.Atomic layer deposition(ALD)is an advanced technique which can provide conformal,thickness-controlled,and high-quality thin film deposition.Accordingly,studies on ALD based oxide semiconductors have dramatically increased recently.Even so,the relationships between the film properties of ALD-oxide semiconductors and the main variables associated with deposition are still poorly understood,as are many issues related to applications.In this review,to introduce ALD-oxide semiconductors,we provide:(a)a brief summary of the history and importance of ALD-based oxide semiconductors in industry,(b)a discussion of the benefits of ALD for oxide semiconductor deposition(in-situ composition control in vertical distribution/vertical structure engineering/chemical reaction and film properties/insulator and interface engineering),and(c)an explanation of the challenging issues of scaling oxide semiconductors and ALD for industrial applications.This review provides valuable perspectives for researchers who have interest in semiconductor materials and electronic device applications,and the reasons ALD is important to applications of oxide semiconductors.

Influences of different oxidants on characteristics of La_2O_3/Al_2O_3 nanolaminates deposited by atomic layer deposition

A comparative study of two kinds of oxidants（H2O and O3） with the combination of two metal precursors（TMA and La（～iPrCp）3） for atomic layer deposition（ALD） La2O3/Al2O3 nanolaminates is carried out. The effects of different oxidants on the physical properties and electrical characteristics of La2O3/Al2O3 nanolaminates are studied. Initial testing results indicate that La2O3/Al2O3 nanolaminates could avoid moisture absorption in the air after thermal annealing. However, moisture absorption occurs in H2O-based La2O3/Al2O3 nanolaminates due to the residue hydroxyl/hydrogen groups during annealing. As a result, roughness enhancement, band offset variation, low dielectric constant and poor electrical characteristics are measured because the properties of H2O-based La2O3/Al2O3 nanolaminates are deteriorated. Addition thermal annealing effects on the properties of O3-based La2O3/Al2O3 nanolaminates indicate that O3 is a more appropriate oxidant to deposit La2O3/Al2O3 nanolaminates for electron devices application.

Influences of different oxidants on the characteristics of HfAlO_x films deposited by atomic layer deposition

A comparative study of two kinds of oxidants（H2O and O3） with the combinations of two metal precursors [trimethylaluminum（TMA） and tetrakis（ethylmethylamino） hafnium（TEMAH）] for atomic layer deposition（ALD） hafnium aluminum oxide（HfAlOx） films is carried out.The effects of different oxidants on the physical properties and electrical characteristics of HfAlOx films are studied.The preliminary testing results indicate that the impurity level of HfAlOx films grown with both H2O and O3 used as oxidants can be well controlled,which has significant effects on the dielectric constant,valence band,electrical properties,and stability of HfAlOx film.Additional thermal annealing effects on the properties of HfAlOx films grown with different oxidants are also investigated.

Influences of different structures on the characteristics of H_2O-based and O_3-based La_xAl_yO films deposited by atomic layer deposition

H_2O-based and O_3-based La_xAl_yO nanolaminate films were deposited on Si substrates by atomic layer deposition（ALD）. Structures and performances of the films were changed by different barrier layers. The effects of different structures on the electrical characteristics and physical properties of the La_xAl_yO films were studied. Chemical bonds in the La_xAl_yO films grown with different structures and different oxidants were also investigated with x-ray photoelectron spectroscopy（XPS）. The preliminary testing results indicate that the La_xAl_yO films with different structures and different oxidants show different characteristics, including dielectric constant, equivalent oxide thickness（EOT）, electrical properties, and stability.

Plasma-Enhanced Atomic Layer Deposition of Amorphous Ga_(2)O_(3) for Solar-Blind Photodetection

Wide-bandgap gallium oxide(Ga_(2)O_(3))is one of the most promising semiconductor materials for solar-blind(200 nm to 280 nm)photodetection.In its amorphous form,amorphous gallium oxide(a-Ga_(2)O_(3))maintains its intrinsic optoelectronic properties while can be prepared at a low growth temperature,thus it is compatible with Si integrated circuits(ICs)technology.Herein,the a-Ga_(2)O_(3) film is directly deposited on pre-fabricated Au interdigital electrodes by plasma enhanced atomic layer deposition(PE-ALD)at a growth temperature of 250°C.The stoichiometric a-Ga_(2)O_(3) thin film with a low defect density is achieved owing to the mild PE-ALD condition.As a result,the fabricated Au/a-Ga_(2)O_(3)/Au photodetector shows a fast time response,high responsivity,and excellent wavelength selectivity for solar-blind photodetection.Furthermore,an ultra-thin MgO layer is deposited by PE-ALD to passivate the Au/a-Ga_(2)O_(3)/Au interface,resulting in the responsivity of 788 A/W(under 254 nm at 10 V),a 250-nm-to-400-nm rejection ratio of 9.2×10^(3),and the rise time and the decay time of 32 ms and 6 ms,respectively.These results demonstrate that the a-Ga_(2)O_(3) film grown by PE-ALD is a promising candidate for high-performance solar-blind photodetection and potentially can be integrated with Si ICs for commercial production.

Electrical Properties of Compositional Al2O3 Supplemented HfO2 Thin Films by Atomic Layer Deposition

With advanced research for dielectrics including capacitors in DRAMs, decoupling filters in microcircuits and insulating gates in transistors, a lot of demand for the new challenging of high-k materials in semiconductor industries has been emerged. This study explores and addresses the experimental approach for composite materials with one of the major concerns of high capacitance, and low leakage, as well as ease of integration technology. The characteristics of Al2O3 supported HfO2 (AHO) thin films for a series of different Hf ratios with Al2O3 dielectrics by atomic layer deposition demonstrated as a candidate material. A composite AHO films with the homogeneous compositions of Al and Hf atoms into the Al-Hf-O mixed oxide system could stabilize the polycrystalline structure with increasing of dielectric constant (k) and decreasing of leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. 70 nm thick AHO thin films with different composition of Al and Hf contents were prepared by atomic layer deposition technique on titanium nitride (TiN) and silicon dioxide (SiO2) coated Si substrates. Photolithography and metal lift-off technique were used for the device fabrication of the metal-insulator-metal (MIM) capacitor structures. AHO films on TiN/SiO2/Si were measured by semiconductor analyzer and source/ measure system with probe station in the voltage range from -5 to 5 V with a frequency range from 10 kHz to 1 MHz were used to conduct capacitance-voltage (C-V) measurements with low/medium frequency range and current-voltage (I-V) measurements. It was found that Au/AHO/TiN/SiO2/Si MIM capacitors demonstrate a capacitance density of 1.5 - 4.5 fF/μm2 at 10 kHz, a loss tangent of 0.02 - 0.04 at 10 kHz, dielectric constant of 11.7 - 35.5 depending on the composition and a low leakage current of 1.7 × 10-9 A/cm2 at 0.5 MV/cm at room temperature. The acquired experimental results could show the possibility of compositional alloy thin films that could potentially replace or open new market for high-k challenges in semiconductor technology.

Effect of Annealing on Aluminum Oxide Passivation Layer for Crystalline Silicon Wafer

The surface of silicon was passivated by A1203 and acidify using nitric acid with SiOx as the bi-layer, it was expected that hydrogen bonding reduce interface states and negative field effect which yields maximum passivation. By optimizing the thickness of passivation layer and annealing condition, the minority carrier lifetime of p-type single crystalline Czochralski wafer could be improved from 10 μs to 190 μs. The formation and variation of hillock defect on passivation layer was founded to be affected by the thermal annealing temperature. For the purpose of obtaining high minority carrier lifetime and low hillock defect density simultaneously, using a lower heating and cooling speed in thermal annealing process is suggested.

Atomic layer deposition to heterostructures for application in gas sensors

Atomic layer deposition(ALD) is a versatile technique to deposit metals and metal oxide sensing materials at the atomic scale to achieve improved sensor functions. This article reviews metals and metal oxide semiconductor(MOS) heterostructures for gas sensing applications in which at least one of the preparation steps is carried out by ALD. In particular, three types of MOS-based heterostructures synthesized by ALD are discussed, including ALD of metal catalysts on MOS, ALD of metal oxides on MOS and MOS core–shell(C–S) heterostructures.The gas sensing performances of these heterostructures are carefully analyzed and discussed.Finally, the further developments required and the challenges faced by ALD for the synthesis of MOS gas sensing materials are discussed.

Atomic layer deposition enabling higher efficiency solar cells:A review

Atomic layer deposition(ALD)can synthesise materials with atomic-scale precision.The ability to tune the material composition,film thickness with excellent conformality,allow low-temperature processing,and in-situ real-time monitoring makes this technique very appealing for a wide range of applications.In this review,we focus on the application of ALD layers in a wide range of solar cells.We focus on industrial silicon,thin film,organic and quantum dot solar cells.It is shown that the merits of ALD have already been exploited in a wide range of solar cells at the lab scale and that ALD is already applied in high-volume manufacturing of silicon solar cells.

Densification of Thin Aluminum Oxide Films by Thermal Treatments

Thin AlOx films were grown on 4H-SiC by plasma-assisted atomic layer deposition (ALD) and plasma assisted electron-beam evaporation at 300°C. After deposition, the films were annealed in nitrogen at temperatures between 500°C and 1050°C. The films were analyzed by X-ray reflectivity (XRR) and atomic force microscopy (AFM) in order to determine film thickness, surface roughness and density of the AlOx layer. No differences were found in the behavior of AlOx films upon annealing for the two different employed deposition techniques. Annealing results in film densification, which is most prominent above the crystallization temperature (800°C). In addition to the increasing density, a mass loss of ~5% was determined and attributed to the presence of aluminum oxyhydroxide in as deposited films. All changes in film properties after high temperature annealing appear to be independent of the deposition technique.

Review of recent progresses on flexible oxide semiconductor thin film transistors based on atomic layer deposition processes

The current article is a review of recent progress and major trends in the field of flexible oxide thin film transistors（TFTs）, fabricating with atomic layer deposition（ALD） processes. The ALD process offers accurate controlling of film thickness and composition as well as ability of achieving excellent uniformity over large areas at relatively low temperatures. First, an introduction is provided on what is the definition of ALD, the difference among other vacuum deposition techniques, and the brief key factors of ALD on flexible devices. Second, considering functional layers in flexible oxide TFT, the ALD process on polymer substrates may improve device performances such as mobility and stability, adopting as buffer layers over the polymer substrate, gate insulators, and active layers. Third, this review consists of the evaluation methods of flexible oxide TFTs under various mechanical stress conditions. The bending radius and repetition cycles are mostly considering for conventional flexible devices. It summarizes how the device has been degraded/changed under various stress types（directions）. The last part of this review suggests a potential of each ALD film, including the releasing stress, the optimization of TFT structure, and the enhancement of device performance. Thus, the functional ALD layers in flexible oxide TFTs offer great possibilities regarding anti-mechanical stress films, along with flexible display and information storage application fields.

Characteristics of atomic layer deposited transparent aluminumdoped zinc oxide thin films at low temperature

Various aluminum-doped zinc oxide （AZO） films were prepared on Si substrate by atomic layer de- position （ALD） at 100 ℃. The effect of the composition of AZO films on their electrical, optical characteristics, structural property and surface topography was investi- gated. The appearance of electrical resistivity shows their semiconducing properties. In most of the visible light band, all the AZO films present transparency of more than 80 %. A1 doping suppresses the AZO film crystallization. When the A1 doping concentration increases up to 3.95 at%, the AZO film has some small multicrystal grains with random orientation. A1 doping improves the roughness of i-ZnO film. The root mean square （RMS） roughness of samples prepared by ALD is much smaller than that pre- pared by radio-frequency magnetron sputtering reported.

Electrical and Corrosion Properties of Titanium Aluminum Nitride Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition

Titanium-aluminum-nitride（TiAlN） films were grown by plasma-enhanced atomic layer deposition（PEALD）on 316 L stainless steel at a deposition temperature of 200 °C. A supercycle, consisting of one AlN and ten TiN subcycles, was used to prepare TiAlN films with a chemical composition of Ti（0.25）Al（0.25）N（0.50）. The addition of AlN to TiN resulted in an increased electrical resistivity of TiAlN films of 2800 μΩ cm, compared with 475 μΩ cm of TiN films, mainly due to the high electrical resistivity of AlN and the amorphous structure of TiAlN. However, potentiostatic polarization measurements showed that amorphous TiAlN films exhibited excellent corrosion resistance with a corrosion current density of 0.12 μA/cm^2, about three times higher than that of TiN films, and about 12.5 times higher than that of 316 L stainless steel.

Engineering the surface of LiCoO2 electrodes using atomic layer deposition for stable high-voltage lithium ion batteries

Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles.Here,we deposited chemically inert and ionically conductive LiAlO2 interfacial layers on LiCoO2 electrodes using the atomic layer deposition technique.During prolonged cycling at high-voltage,the LiAlO2 coating not only prevented interfacial reactions between the LiCoO2 electrode and electrolyte,as confirmed by electrochemical impedance spectroscopy and Raman characterizations,but also allowed lithium ions to freely diffuse into LiCoO2 without sacrificing the power density.As a result,a capacity value close to 200 mA＆#183;h＆#183;g-1 was achieved for the LiCoO2 electrodes with commercial level loading densities,cycled at the cut-off potential of 4.6 V vs.Li＋/Li for 50 stable cycles;this represents a 40% capacity gain,compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs.Li＋/Li.

In vitro corrosion resistance of a Ta2O5 nanofilm on MAO coated magnesium alloy AZ31 by atomic layer deposition

Micro-arc oxidation(MAO)coating with outstanding adhesion strength to Mg alloys has attracted more and more attention.However,owing to the porous structure,aggressive ions easily invaded the MAO/substrate interface through the through pores,limiting long-term corrosion resistance.Therefore,a dense and biocompatible tantalum oxide(Ta2O5)nanofilm was deposited on MAO coated Mg alloy AZ31 through atomic layer deposition(ALD)technique to seal the micropores and regulate the degradation rate.Surface micrography,chemical compositions and crystallographic structure were characterized using FE-SEM,EDS,XPS and XRD.The corrosion resistance of all samples was evaluated through electrochemical and hydrogen evolution tests.Results revealed that the Ta2O5 film mainly existed in the form of amorphousness.Moreover,uniform deposition of Ta2O5 film and effective sealing of micropores and microcracks in MAO coating were achieved.The current density(icorr)of the composite coating decreased three orders of magnitude than that of the substrate and MAO coating,improving corrosion resistance.Besides,the formation and corrosion resistance mechanisms of the composite coating were proposed.

Atomic layer deposition of core-shell structured V_(2)O_(5)@CNT sponge as cathode for potassium ion batteries

Potassium-ion batteries(KIBs)represent one of the most promising alternatives to lithium-ion batteries(LIBs)considering the potential low cost and abundant potassium resource.In this work,we demonstrate a core-shell structured sponge cathode for KIBs,where amorphous V_(2)O_(5) uniformly coats on carbon nanotube(CNT)sponge via atomic layer deposition(ALD).The V_(2)O_(5)@CNT sponge shows several advantages as cathode:(1)the three-dimensional(3D)conductive network of CNT sponge offers a fast electron transport pathway,(2)the porous nature and high surface area of CNT sponge enables enough access for electrolyte to V_(2)O_(5),(3)the amorphous structure of V_(2)O_(5) offers a fast kinetics upon K-ion insertion/deinsertion.The V_(2)O_(5)@CNT sponge cathode delivers a high capacity of 206mA h/g and moderate cycling and rate performance in common carbonate-based electrolyte system.

Influence of surface preparation on atomic layer deposition of Pt films

We report Pt deposition on a Si substrate by means of atomic layer deposition（ALD） using（methylcyclopentadienyl） trimethylplatinum（CH_3C_5H_4Pt（CH_3）_3） and O_2.Silicon substrates with both HF-last and oxidelast surface treatments are employed to investigate the influence of surface preparation on Pt-ALD.A significantly longer incubation time and less homogeneity are observed for Pt growth on the HF-last substrate compared to the oxide-last substrate.An interfacial oxide layer at the Pt-Si interface is found inevitable even with HF treatment of the Si substrate immediately prior to ALD processing.A plausible explanation to the observed difference of Pt-ALD is discussed.

Microstructure of Epitaxial Er2O3 Thin Film on Oxidized Si （111） Substrate

Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction （GIXRD）, atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystal domains. The interplanar spacing d in-plane residual strain tensor ell and the strain relaxation degree ε are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulk Er2O3. In-plane strains in three sets of planes, i.e. （440）, （404）, and （044）, are isotropic.